The present invention relates to spectral measurement devices and more particularly to a process for manufacturing a diffraction grating having a low blaze angle.
A diffraction grating is the key element of most spectral measurement devices. The diffraction grating is an optical device which creates a spectrum by the diffraction of a beam of electromagnetic radiation (most typically light) through a grating consisting of closely and regularly spaced parallel grooves incised in some substantially planar surface. In a grating used in optical transmission, the surface is typically glass or plastic. When used for reflection, a polished aluminum or metal mirror is used for the surface. One type of reflective grating commonly used for infrared wavelengths are echelette gratings. These gratings or grooves take the form of a series of stepped optically flat surfaces inclined at some specified angle to reflect the majority of energy in one direction and into a specific diffractive order. The angle that the stepped surfaces make with the front surface of the grating (the blaze angle), together with the distance between steps (for defining the pitch of the grating), and length of each stepped surface, specify the primary characteristics of the grating.
In the past, such gratings have typically been made mechanically using a device called a ruling engine. The ruling engine consists of a precisely shaped diamond cutter mounted on a two-axis slide assembly so that each groove of the grating is cut by successive passes of the diamond tool across the metal blank. The finished grating can be used as is, or as a master for the production of replicated gratings. This technique works well for many types of gratings, but has not been capable of producing reflective gratings with low blaze angles.
It is accordingly a primary object of the present invention to provide a process for manufacturing spectral gratings having low blaze angles.